1. Field of the Invention
The present invention relates to the conveyance of developer. In particular, the present invention relates to an electrophotographic image forming apparatus including a process cartridge and is suitable for an electrophotographic color-image-forming apparatus.
Herein, the term “electrophotographic image forming apparatus” refers to an apparatus that forms an image on a recording medium by an electrophotographic image forming method. Exemplary electrophotographic image forming apparatuses include an electrophotographic copier, an electrophotographic printer (such as a laser beam printer and a light-emitting-diode (LED) printer), a facsimile apparatus, and a word processor.
The term “process cartridge” refers to a cartridge including a charging device, a developing portion, a cleaning device, and an image bearing member. The cartridge is attachable to and detachable from a main body of the electrophotographic image forming apparatus. The process cartridge attachable to and detachable from the body of the electrophotographic image forming apparatus may be a cartridge unit including an image bearing member and at least one of the charging device, the developing portion, and the cleaning device.
The term “developing device” refers to a unit attachable to and detachable from the main body of an image forming apparatus and including a developing portion that develops a latent image on an image bearing member, a developing-portion frame that supports the developing portion, and other components associated with the developing portion. The developing device is also referred to as developing cartridge or developing unit, according to need.
The term “developer container” refers to a container that stores developer to be used in an electrophotographic image forming process and includes a conveying device that conveys the developer stored therein, and so forth.
2. Description of the Related Art
In a known image forming apparatus employing an electrophotographic image forming process, a cartridge system is employed in which cartridges such as a developing cartridge and a process cartridge are attachable to and detachable from the body of the image forming apparatus. Such a cartridge system may have a function of indicating the remaining number of printable pages so that the user can replace the cartridge with a new one at an appropriate timing. To add such a function to the cartridge system, the amount of developer remaining in the cartridge needs to be detected or estimated. To do so, several methods have already been proposed.
One of those proposed methods is a light-transmission remaining-developer-amount-detecting method. In this method, an optical path passing through a developer chamber is provided between a light-emitting device such as an LED and a light-receiving device such as a phototransistor that are attached to the body or any other component of the image forming apparatus, and the remaining amount of developer is calculated from how long the developer has blocked light.
In an exemplary light-transmission remaining-developer-amount-detecting method (disclosed by Japanese Patent Laid-Open No. 2003-131479), an emission-side light-guiding member and a reception-side light-guiding member are provided to a developer container unit so as to guide detecting light into a developer chamber. The emission-side light-guiding member guides the detecting light, emitted from a light-emitting device such as an LED, into the developer chamber. The reception-side light-guiding member guides the detecting light that has been transmitted through the developer chamber toward a light-receiving device, such as a phototransistor, provided on the outside of the developer chamber.
In another exemplary method (disclosed by Japanese Patent Laid-Open No. 2003-167490), a light-guiding member as a unit including an emission-side light-guiding member and a reception-side light-guiding member is provided in a longitudinal central area of a developer chamber.
Furthermore, a known developing device includes a development chamber and a developer chamber. In the development chamber, a developer bearing member for supplying developer to a photosensitive drum and a developer supplying member for supplying the developer to the developer bearing member are provided. The developer to be supplied to the development chamber is stored in the developer chamber. In such a device, the developer chamber is positioned below the development chamber in the gravitational direction. Therefore, the developer needs to be conveyed against the gravitational force.
There are some known methods of conveying developer from a developer chamber to a development chamber provided above the developer chamber. In one of those methods, the developer is conveyed with a rotational motion of a flexible sheet. Another method employs a sheet member that conveys developer from a developer chamber to a development chamber while passing two positions: a deformation position where the sheet member is elastically deformed while being in contact with the sidewall of the developer chamber, and a restoration position where the elastically deformed sheet member is released. In each of the methods, the developer is conveyed by utilizing a force (restoring force) generated when the sheet member that has been deformed restores its original form (see Japanese Patent Laid-Open No. 2011-253203 and Japanese Patent Laid-Open No. 2008-209897).
In such known proposals, however, to reduce the size of the cartridge, the light-guiding members are provided on the upstream side with respect to the boundary between the deformation position and the restoration position in the direction of rotation of the sheet member. Furthermore, the light-guiding members include protrusions provided on the sidewall of the developer chamber. Therefore, when the sheet member, which is carrying the developer, goes over the protrusions of the light-guiding members, some of the developer may fall off the sheet member at the contact with the protrusions, and the amount of developer on the sheet member that is to be conveyed to the development chamber may be reduced. That is, the amount of developer on the sheet member may be reduced before the sheet member passes the boundary between the deformation position and the restoration position.